In modern bullet firing firearms, metal bullets are expelled through the rifled barrel of the firearm as a result of a percussive charge being detonated on the side of the bullet opposite the discharge end of the barrel. For stability, the bullet is caused to rotate about its longitudinal axis by rifling within the barrel. As a consequence, frictional contact between the bullet and the barrel is substantial.
Further, bullets are typically made of metal with hunting bullets being formed of a lead body or core with or without jacketing by another metal as for example, a copper jacket. Military ammunition will typically use steel jacketed bullets, which are highly erosive.
In all events, the friction between the bullets traveling through the barrel and the barrel itself causes wear on the interior of the barrel which shortens its life and, at some point in time will begin to interfere with the accuracy of the firearm. Furthermore, barrel fouling frequently occurs from metal scraped from the surface of the bullet or the jacket as a result of the friction. Prolonged firing of the firearm without cleaning can result in a loss of accuracy when the barrel is fouled.
The peak pressure generated by the detonating charge is also affected by the frictional characteristics involved. The greater the friction between the bullet and the barrel, the higher the peak pressure. In order to achieve safety in the firearm, in many instances, the presence of high friction requires the use of a lesser charge in the cartridge so that peak pressure is reduced to a safe value. This may lead to lower bullet velocities which in turn means that bullet trajectory will become more curved.
To overcome these difficulties, it has long been recognized that lubricant may be applied to a bullet to reduce the friction. One lubricant that has been proposed is molybdenum disulfide. As a means of applying molybdenum disulfide, Martin, in U.S. Letters Pat. No. 4,454,175 issued Jul. 12, 1984, proposes placing molybdenum disulfide, the bullets to be coated, steel balls and a fibrous medium in a tumbler. The bullets are tumbled with the steel balls, molybdenum disulfide and/or the fibrous medium for 2-6 hours, dependant upon the thickness of the coating desired.
The resulting bullets are said to increase accuracy and to reduce metal fouling of the barrel. However, because of the long tumbling time, the process is extremely time consuming and not economically viable.
The present invention is directed to overcoming one or more of the above problems.